"How many friends can Xbox One users have?" Sony Computer Entertainment America president Jack Tretton asked. "One thousand, Mr. Tretton," his assistant responded. "What's two times bigger than that?" Tretton asked, too busy remembering, longing for a crowded convention center cheering his every word to do arithmetic. "Two thousand, Mr. Tretton," his assistant answered.
"PS4 users can have 2,000 friends," Tretton said after a few seconds, and grinned.
At least, that's roughly how we think the decision was made. Other common PlayStation 4 questions are cleared up in this official video, like whether PS4 has party chat (it does), and even the specific shade of black used for PS4's design (hint, it's not "Piano" any more, but it is still Black).